Nutrient selection and injection are controlling factors in many subterranean microbial processes. In order to achieve this specific objective, e.g. microbial enhanced oil recovery (MEOR) and bioremediation processes, the microorganisms utilized must be metabolically active and nutritiously sustained.
Numerous microorganisms suitable for achieving various microbial objectives in subterranean formations are known in the art. In order to achieve a specific microbial objective, suitable microorganisms can be selected and injected into the subterranean formation. Oftentimes, however, endogenous microorganisms well suited for achieving a particular microbial objective, are already present within the formation.
It is well established that these microorganisms basically require three utilizable nutrient sources to remain active. These sources are a carbon source, a nitrogen source, and a phosphorus source. The specificity of each reservoir will determine which nutrients are needed, as a reservoir may be deficient in any or all of the above nutrients. A common deficiency, however, is that of phosphorus, thus mandating that a phosphorus source be injected to sustain microbial activity. Inorganic phosphates are well known in the art for use as phosphorus nutrients, however, a problem associated with their use is the indepth transportation of these phosphates into the reservoir. The difficulty encountered in the transportation of inorganic phosphate is due to some extent to high concentration of divalent cations, and in particular calcium, found in reservoirs which complexes with the phosphates to render the phosphates insoluble and less able to be easily transported due to greater retention of the phosphate precipitate in the rock matrix. Thus, indepth penetration of the phosphate is not readily achieved.
Without an efficient method for indepth penetration of nutrients, excessive utilization and depletion of nutrients by microorganisms located at or near the injection borehole occurs. Excessive utilization and depletion of nutrients by microorganisms located in the vicinity of the borehole operates to prevent nutrient distribution and create excessive plugging in the vicinity of the borehole, i.e. faceplugging.
Therefore, a method to facilitate the indepth transport of the phosphorus nutrient source by increasing the solubility of the phosphates and/or dissolving acid soluble minerals that are responsible, at least in part, for the phosphate retention would be a significant contribution to the art.
It is therefore an object of this invention to provide a method for facilitating the transportation of phosphorus nutrient sources deep within the reservoir to achieve indepth nutrient distribution and to prevent excessive plugging in the vicinity of the borehole.
It is another object of this invention to provide a method of transport for inorganic phosphates whereby their solubility is increased and they are less retainable by rock matrix of the reservoir.
It is a further object of this invention to provide a method for indepth phosphate transportation whereby acid soluble minerals are dissolved thus decreasing phosphate retention in the rock matrix of the reservoir.
These and other objects of the present invention will become apparent upon inspection of the disclosure and the claims herein provided.